Chemical polishing solution and method



the metal.

Patented Oct. 19, 1954 CHEMICAL POLISHIN METH G SOLUTION AND OD Bo-ShinR0, Tokyo, Japan, assignor to Khe-Beng I Chiong, San Diego, Calif.

No Drawing. Application April 15, 1952,

. Serial No. 282,484

10 Claims.

This invention relates to an improved method of polishing aluminum,aluminum alloys and steels, involving the use of chemical solutions.

Heretofore, certain solutions have been used for polishing copper,aluminum and aluminum alloys and pickling solutions for steel are wellknown. For example, nitric acid has been used for polishing copper andits alloys, and metaphosphoric acid in a water solution and hydrofluoricacid have been used to produce mirrorlike surfaces on aluminum. Thetheory of the above mentioned chemical means for obtaining a smooth.polished surface is that under certain conditions difficultly soluble orinsoluble salts are formed which adhere to the slightly depressed partsof the surface 'of the metal. This allows the action. of the solution onthe raised portion to produce an even surface. This is different frommerely cleaning the surface which is common in the pickling action ofsaid metals.

It is an object of the present invention to produce a polished'ormirror-like surface on certain metals commonly classed as non-reactive.

It is also an object of the present invention to produce such a surfaceby chemical means in a comparatively short length of time.

Generally speaking, this process contemplates the use of a bathcontaining reactive chemicals which, when contacted with a metal surfacethat is more or less uneven, will act on the metal to produce a smooth,even mirror-like surface on Such steels as stainless steel and othersteels containing large percentages of chromium, which are verydifiicult to react with ordinary polishing solutions, respond totreatment with said bath to produce a high polish in a short space oftime. Ordinary carbon steels also react with this solution to producethe desired effect.

It has been found possible to react aluminum and aluminum alloys withsuitable baths containing the solutions that are the subject matter ofthis invention.

According to the invention, this bath is maintained at a temperature of120 C. to 260 C. This temperature must of necessity be within themelting point of the ingredients of the bath so as to maintain the bathin a liquid condition, and the time of immersion of the metal in thebath depends upon the temperature of the bath, the higher thetemperature the less time the metal must be in contact with the bath toproduce the desired results.

As may be seen in the examples, certain specific emperatures and certaintimes of immersion 2 will give the desired results, but if thetemperature is raised the time may be shortened.

It has been found that under suitable temperature conditions a solutioncontaining specific forms of an acid having phosphorus in itscomposition is effective in polishing the metals referred to above. Thetype of phosphorus containing acids that have been found desirable arethe two types containing the least amount of water of composition, thatis, meta-phosphoric and Pym-phosphoric acid. Meta-phosphoric acid is thephosphoric acid anhydride with one molecule of water and pyro-phosphoricacid is the anhydride with two molecules of water. It has beenfoundundesirable to use ortho-phosphoric acid, which is the'an hydride withthree molecules of water. Phosphoric acid is not desirable as-itproduces an effect known as parkerizing.

Pyro-phosphoric acid is therefore preferred, but the meta form may beused. A small quantity of an organic acid, such. as tartaric acid oroxalic acid, hastens the reaction and has the desired results. Intreating certain types of steel it is also desirable to include a smallamount of ferrous sulphate, or as a substitute therefor, a small amountof sulfuric acid.

To better illustrate the invention as described above, the followingexamples are included. This invention is not to be limited to theseexamples, which are cited primarily as illustrations:

EXAMPLE I (1) Example of carbon steel H4P2O7 or HPOs 100 cc. or weight100 g. CeHaO"! OI (COOH) 2 2 g. Temperature 160 C. Time 5 sec.

EXAMPLE II (2) Example of stainless steel and Cr steel H4P2O'1 or HPOs100 cc. or Weight 100 g. CsHsO'z 2 g. 1 F6804 5 g.

Temperature 200 C. Time 15 sec.

EXAMPLE III (3) Example of Al, and Al-alloys H4P2Oq or HPO3 100 cc. orweight 100 g. (COOH)2 10 g. Temperature 120 C.

Time 7 sec.

The term polishing as used in this specification does not mean cleaning,as is usual in common pickling processes, but denotes a chemicalreaction on the surface of the metal to remove the raised portions fromthe surface and to give a highly polished mirror-like surface whichdiffers from an etched surface. Etching usually results in an unevensurface produced by removing certain constituents preferentially.

The novel solution disclosed in the present application acts rapidly toproduce the highly polished surface desired. It reacts with aluminum,aluminum alloys and steel to produce the desired surface in a fewseconds and allows the use of continuous methods of handling theproducts from one bath to another, and gives a high lustre on astainless steel which has heretofore been unobtainable except afterprolonged treatment.

What is claimed is:

1. The method of producing a high lustre on a metal selected from thegroup consisting of carbon steel, special steel, aluminum, and aluminumalloys, which consists of immersing said metal in an anhydrous bath at atemperature of 120 C. to 260 C. for a period of time less than 60seconds, said bath consisting of an acid selected from the groupconsisting of meta-phosphoric acid and pyrophosphoric acid and at leastone substance selected from the group consisting of tartaric acid,oxalic acid, ferrous sulphate and sulfuric acid.

2. A method of polishing carbon steel which comprises contacting thesteel for about 5 seconds at a temperature of 160 C. with an anhydroussolution containing about 100 parts of an acid selected from the groupconsisting of metaphosphoric acid and pyrophosphoric acid and about 2parts of an acid selected from the group consisting of tartaric acid andoxalic acid.

3. A method of polishing stainless steel which comprises immersing thesteel in an anhydrous bath at a temperature of 200 C. for about 15seconds, said bath consisting of 100 parts of an acid selected from thegroup consisting of metaphosphoric acid and pyrophosphoric acid, about 42 parts of tartaric acid and about 5 parts of ferrous sulphate.

4. A method of polishing aluminum and aluminum alloys which comprisesimmersing the metal in an anhydrous bath for about 7 seconds at atemperature of 120 C., said bath consisting of parts of an acid selectedfrom the group consisting of meta-phosphoric acid and pyrophosphoricacid and 10 parts of oxalic acid.

5. A bath for polishing stainless steel containing ferrous sulphate, anacid selected from the group consisting of meta-phosphoric acid andpyro-phosphoric acid and at least one substance selected from the groupconsisting of oxalic acid, tartaric acid, and sulfuric acid, said bathbeing maintained at a temperature of C. to 260 C.

6. An anhydrous composition for polishing carbon steel consisting of 100parts of metaphosphoric acid and about 2 parts of tartaric acid.

7. An anhydrous composition for polishing carbon steel consisting of 100parts of pyrophosphoric acid and about 2 parts of oxalic acid.

8. .An anhydrous composition for polishing stainless steel consisting of100 parts of metaphosphoric acid and 2 parts of tartaric acid and about5 parts of ferrous sulphate.

9. An anhydrous composition for polishing stainless steel consisting of100 parts of pyrophosphoric acid, about 2 parts of tartaric acid andabout 5 parts of ferrous sulphate.

10. An anhydrous composition for polishing an aluminum containing metalcomprising 100 parts of pyrophosphoric acid and 10 parts of oxalic acid.

References Cited in the file of this patent UNITED STATES PATENTS NumberName V Date 2,334,699 Faust Nov. 23, 1943 2,386,078 Weisberg et a1. Oct.2, 1945 2,412,186 Whitehouse et al. Dec. 3, 1946 2,446,060 Pray et alJuly 2'7, 1948 2,461,228 Miles Feb. 8, 1949

1. THE METHOD OF PRODUCING A HIGH LUSTRE ON A METAL SELECTED FROM THEGROUP CONSISTING OF CARBON STEEL, SPECIAL STEEL, ALUMINUM, AND ALUMINUMALLOYS, WHICH CONSISTS OF IMMERSING SAID METAL IN AN ANHYDROUS BATH AT ATEMPERATURE OF 120* C. TO 260* C. FOR A PERIOD OF TIME LESS THAN 60SECONDS, SAID BATH CONSISTING OF AN ACID SELECTED FROM THE GROUPCONSISTING OF MELA-PHOSPHORIC ACID AND PYROPHOSPHORIC ACID AND AT LEASTONE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF TARTARIC ACID,OXALIC ACID, FERROUS SULPHATE AND SULFURIC ACID.